1. Field of the Invention
The present invention relates to a computer aided engineering (CAE) system and, more particularly, to a CAE system for effecting the heat analysis of electronic equipment by a finite difference method, node method or similar method.
2. Description of the Prior Art
Design analysis calculations using a computer is extensively used today and has come to implement the versatile inspection of the behavior of an object to be designed. Especially, the application of a CAE system to the analysis of strength, vibration and other characteristics which relies on structural analysis is extending. On the other hand, heat analysis is generally classified into two kinds of analysis, i.e., heat conduction analysis dealing with the diffusion of heat in a solid body, and heat fluid dynamics analysis dealing with the movement of a fluid in addition to the diffusion of heat in a solid body. While heat conduction analysis is relatively easy to execute and widely used, the applicability of heat fluid dynamics analysis at the present stage is limited to a particular field and to particular objects having simple configurations since it needs large-scale calculations.
The increase in the package density and processing speed of advanced electronic equipment is so striking, the decrease in the power consumption of individual devices cannot keep abreast of the miniaturization of equipment. In fact, the power consumption per unit volume of equipment is steadily increasing. In these circumstances, traditional heat design relying on intuition and experience does not work and should be replaced with heat analysis and simulation using a computer, as has recently been put into discussion.
Many pieces of electronic equipment are cooled by a stream of air and, therefore, need the previously stated heat fluid dynamics analysis. Typical of methods for heat fluid dynamics analysis are a finite difference method and a finite element method. The problem with such methods is that the zone to be analyzed has to be divided into a difference grating or finite elements. Hence, modeling the internal space of complicated electronic equipment is extremely time and labor-consuming. Moreover, to analyze the behavior of a fluid minutely, the space has to be divided into a difference grating or finite elements extremely minutely, resulting in the need for a prohibitive preprocessing time. For this reason, the finite difference method and finite element method are scarcely used for practical designing purposes.
A method generally referred to as a node method is predominant in the heat analysis of electronic equipment. The node method divides the internal space of electronic equipment relatively roughly into blocks, defines representative points or so-called nodes at the center of the individual blocks, and then determines the energy balance amoung the nodes by solving simultaneous equations relating to the nodes. The advantage of the node method is that the propagation of heat from a solid body to a fluid such as air can be represented roughly in terms of heat transfer rate. Regarding heat transfer rate, a number of equations for analysis and experimental equations have been reported in the field of heat transfer engineering. By using any of such equations, it is possible to estimate the propagation of heat without resorting to the strict calculations of the behavior of a fluid, i.e., without solving Navier-Stokes equation. Hence, accurate results are achievable by relatively small-scale calculations.
However, the state of the art node method is not satisfactory in that the resultant model is much removed from the actual image of analyzed equipment since it represents the individual nodes by a heat equivalent circuit connected by heat resistors or a ventilation equivalent circuit connected by ventilation resistors. With the node method, therefore, it is difficult to generate a model for analysis by using CAD data with which the finite element method is practicable. Another drawback particular to the node method is that the resistances of heat resistors or those of ventilation resistors cannot be determined unless adequate equations are selected with reference to experimental equations or similar equation, requiring expert knowledge on heat transfer theories.
Referring to FIG. 6, a heat analysis procedure using the conventional node method is shown in a flowchart. The procedure will be described with reference also made to FIGS. 7A to 7D which illustrates a modeling sequence specifically. As shown in FIG. 6, the conventional method begins with a step 101 of simplifying a model of interest and dividing the simplified model into blocks. For example, as shown in FIG. 7A, the interior of electronic equipment is represented by such blocks. The equipment shown in FIG. 7A has a housing 120 which is provided with a blower or fan 122 and a ventilation opening 123. Various units 121 are accommodated in the housing 120. While the equipment has a tridimensional configuration in practice, let it be represented by a bidimensional configuration for the simplicity of description. As shown in FIG. 7B, the areas, or blocks in the tridimensional aspect, defined by dividing the entire space in the step S101 each has a rectangular or triangular shape (hexahedron or any other configuration in the tridimensional aspect). A node 130 is defined at the center of gravity of each of such divided blocks.
As shown in FIG. 7C, the nodes of the blocks 131 belonging to the fluid portions of the equipment, i.e., fluid nodes are connected together by ventilation resistors 140 to determine ventilation resistances (step 102). Specifically, the ventilation resistors 140 are determined by calculating on the basis of the ventilation cross-sectional areas of the blocks 131 represented by the nodes which are located at opposite ends of the individual resistors, the distances between associated nodes, the differences in cross-sectional area, etc. For such calculations, a reference has to be made to a great number of equations (103).
Subsequently, the rate, pressure, and other boundary conditions of air section 141 where the blower 122 is located are set up (104), and then simultaneous equations are solved to determine pressures (105). As a result, the pressures at the individual nodes and the rate of air to flow between each nearby nodes are produced (106). Since the equivalent heat conductivity between nearby nodes is calculated from the rate of air between them, the ventilation equivalent circuit shown in FIG. 7C and already constructed can be directly substituted for a heat equivalent circuit in the fluid portions if the heat conductivity is used as a resistance.
As shown in FIG. 7D, the heat conduction resistors 150 particular to the inside of solid bodies 121 which are disposed in the casing 120 and the heat transfer resistors 151 and 152 from the solid bodies 121 to the fluid are calculated and added to the above-mentioned heat equivalent circuit. As a result, a heat equivalent circuit representative of the entire equipment is completed. This part of the processing involves many kinds of inspections, e.g., referencing the physical properties of the individual materials (108) to calculate the heat resistances (107) and referencing equations (110) to calculate heat transfer or propagation coefficients (109).
After the heat equivalent circuit network has been generated, boundary temperature conditions such as the amount of heat generation are set up (111), and then simultaneous equations are solved to determine temperatures (112).
In the specific procedure shown in FIG. 6, only the steps 105 and 106 for setting up a coefficient matrix and the step 112 for solving simultaneous equations can be assigned to a computer, i.e., the rest of the procedure has to be done mainly by manual operations. Since the node method solves problems relating to heat in exactly the same manner as it deals with electric circuitry, software for general analysis is often used to execute the above-mentioned part of the procedure which can be implemented by a computer.
As stated above, the conventional heat analysis, whatever the method for implementing it may be, is difficult to practice when it comes to the interior of electronic equipment. Even the node method which is the most general-purpose scheme has some serious problems. Namely, the node method requires not only much manual work but also a great number of analyzing steps, needs highly expert knowledge such as for the calculation of heat resistances, has difficulty in calculating natural convection, and cannot easily implement calculations which take account of the characteristics of a blower or fan.
At the present stage of technologies, therefore, it is almost impossible to effect practical heat analysis of electronic equipment.
The applicable range of heat analysis may be limited to electronic equipment having a particular configuration such as one having a plurality of printed circuit boards arranged in parallel therein, as proposed in the past. In such a case, the entire procedure can be automated by, for example, parameteric input. This kind of scheme, however, is not applicable to various kinds of electronic equipment.
For example, assume that the node method is used to replace the entire electronic equipment 500 shown in FIG. 12A with an extremely rough heat equivalent circuit shown in FIG. 12D or a ventilation equivalent circuit shown in FIG. 12B. Then, the computer treats the equipment 500 as an electric circuit having resistors R and capacitors C which have nothing to do with the actual configuration of the equipment 500. It is therefore difficult to generate a model for the node method by use of the configuration data of general electronic equipment, compared to the finite element method or similar approach.
The electronic equipment 500 shown in FIG. 12A is a unit having printed circuit boards 551 which are regularly arranged in parallel to one another. Although the number and power consumption of printed circuit boards 551, the kind and number of blowers 552 and other factors may differ from one unit to another, all the units are similar in overall configuration. Therefore, the ventilation equivalent circuit shown in FIG. 12B and the heat equivalent circuit shwon in FIG. 12D can be generated if parameters are inputted. For example, a fluid passage 553 defined between nearby printed circuit boards 551 has a ventilation resistor b1 which is calculated from the mounting pitch a1 of the boards 551 and the area a2 of the passage 553. After the ventilation equivalent circuit has been determined, the actual operating point c3 is determined by calculation on the basis of a ventilation characteristic c3 particular to the unit 500 and a static pressure-to-rate characteristic c1 particular to each blower or fan 552, as shown in FIG. 12C. The linear velocity of air at each of various sections of the unit is determined on the basis of the resulted operating point c3, whereby the heat equivalent circuit shown in FIG. 12D is set up. The heat equivalent circuit of FIG. 12D has a printed circuit board d1, solid body nodes defined on the printed circuit board d1, fluid nodes defined in the space between nearby printed circuit boards, solid body heat conduction resistors d4 existing in the printed circuit board, heat conduction resistors d5, and equivalent heat conduction resistors d6 ascribable to the stream of air.
FIG. 13 schematically illustrates a heat analysis CAE system for executing the above-stated analysis procedure. As shown, the heat analysis CAE system has a display 561, an input device 562, a data input/output section 563, a parameter data store 564, a node data generator 565, a ventilation circuit generator 566, a ventilation circuit calculator 567, a heat circuit generator 568, a heat circuit calculator 569, a calculated pressure and rate data store 570, and a calculated temperature data store 571.
The problem with the heat analysis CAE system of the type described is that the operator cannot see at which part of the unit of interest the temperaure is high and at which part the rate of air stream is low directly and, therefore, needs some time to judge the results of calculation. This stems from the fact that parameters representative of the specifications of the unit are inputted as data and cannot be easily related to the calculated temperatures of nodes. Moreover, when the operator inputs wrong parameters by accident, the configuration image is not displayed. Then, it takes a substantial period of time to locate a defective section, and it is difficult to output the calculated configuration of the unit to a utility system such as a computer aided designing (CAD) system.